function [ phi1, phi2, phi3, phi4] = dphi( alpha, betta )
%UNTITLED2 Summary of this function goes here
%   Detailed explanation goes here
k=[cos(alpha)*cos(betta);cos(alpha)*sin(betta);sin(alpha)]; 
lambda=19e-3;

r1=[lambda/4;-lambda/4;0];
r2=[-lambda/4;-lambda/4;0];
r3=[-lambda/4;lambda/4;0];
r4=[lambda/4;lambda/4;0];

phi1=r1.'*k*2*pi/lambda;
phi2=r2.'*k*2*pi/lambda;
phi3=r3.'*k*2*pi/lambda;
phi4=r4.'*k*2*pi/lambda;

end

